Detector for magnetic metal



P 1951 R. A. CHRISTIAN 3,002,149

DETECTOR FOR MAGNETIC METAL i Filed April 22, 1958 3 INVENTOR.

RI CHA RD CHRISTIAN ATTO RN EY 'IIIIIII IIIIIIA 3,002,149 DETECTOR FOR MAGNETIC METAL Richard A. Christian, Milwaukee, Wis. (RR. 2, Box 35, Union Grove, Wis.) Filed Apr. 22, 1958, Ser. No. 730,211 1 Claim. (Cl. 32441) This invention relates to a detector for magnetic metal, and more particularly to a hand-manipulated detector useful in locating ferrous metal concealed by non-magnetic materials.

There are numerous occasions where a need exists to locate a metallic object concealed beneath a surface covering of some type as, for example, the nails in a Wall stud, metal embedded within a tire, etc. To a large extent, such metallic elements have magnetic characteristics (that is, they are ferrous metals), and it is with such metals that this invention is useful.

An object of this invention is to provide a device having utility in the detection of ferrous metal elements embedded in or concealed by non-magnetic coverings. Another object of the invention is in the provision of a device of the character described, which is hand-held and is easy to manipulate and control, and which affords a signal indicia of distinctive character when a ferrous element is located thereby.

Still another object of the invention is in the provision of a magnetic-metal detector of the character described having a rotatable contact surface that enables the same to be rolled over a surface, and which has a signal incorporated therein to indicate the sensing of a ferrous element and the location thereof. A further object of the invention is to provide a detector device of the character described that utilizes either a permanent or electromagnet in the performance of its detection function, and when an electro-magnet is used permits utilization of a convenient power source therefor. Additional objects and advantages of the invention will become apparent as the specification develops.

Embodiments of the invention are illustrated in the accompanying drawings, in which- FIGURE 1 is a perspective view of the detector device embodying the invention;

FIGURE 2 is a longitudinal sectional view taken generally along the longitudinal axis of the rotatable contact member;

FIGURE 3 is a tranverse sectional view taken along the line 3-3 of FIGURE 2;

FIGURE 4 is a broken horizontal sectional view taken along the center plane of the device as shown in FIGURE 1, but in which the rotatable contact element is illustrated in elevation;

FIGURE 5 is a schematic diagram of a circuit employing a permanent magnet; and

FIGURE 6 is a schematic diagram of a modified circuit employing an electro-magnet.

The detector illustrated in its entirety in FIGURE 1 is seen to comprise a frame 10 having a hollow handle 11 secured thereto and equipped at its outer end with a cap 12 which may be threadedly received thereon, as shown in FIGURE 4. The frame 10 is bifurcated or is of yoke-like construction, having spaced ends or legs 14 and 14 that terminate in enlarged, inwardly projecting cylindrical end portions 15 and 15' defining bearings on which a cylinder or roller 16 is rotatably carried.

The cylinder 16 should be constructed of nonmetallic material and may be plastic. Positioned within the roller or cylinder is a magnet 17 which may either be a permanent or electro-magnet, the latter being illustrated and having an electric conductor 18 coiled about a leg thereof. The magnet 17 comprises a pair of longitudinally extending, generally parallel sections 19 and 19' ice which are separated from each other by an insulating body 20, as seen best in FIGURE 3. This figure also makes evident that the lower surfaces of the members 19 and 19 have an arcuate configuration that corresponds to the curvature of the cylindrical roller 16, and thereby permits free rotation of the roller without interference.

The magnet 17 is movably supported by the bearings 15 and 15 by means of a pin 21- threadedly secured to the magnet at 22 adjacent one end thereof, and which projects outwardly therefrom. At the opposite end, the magnet is equipped with a pin 23* threadedly secured thereto as shown at 24. The pin 23 projects outwardly from the magnet a substantial distance, and at its outer end is equipped with a contact pin 25, preferably formed of insulating material. The support pins 21 and 23 extend into vertically oriented slots provided therefor in the bearings 15 and 15, and rest upon resilient members such as springs 26 and 26'. The springs are of helical configuration, and seat at their lower ends against the bearing members. "The springs are constrained for compression along the longitudinal axm thereof by guide pins 27 and 27' carried by the bearing members and which extend into the springs.

Thus, it is apparent that the magnet 17 floats within the cylindrical roller '16, and is normally spaced from the inner surface of the roller as at 28 in FIGURE 3. However, when the roller traverses a metallic object, it is drawn downwardly theretoward with reference to FIG- URES 2 and 3, thereby approaching the surface of the roller 16 and consequently decreasing the space 28. Such downward movement Will be against the biasing action of the coil springs 26 and 26' which urge the magnet toward the normal position thereof shown in FIGURES 2 and 3.

It will be noted that the elongated slot defined in the bearing 15 has an enlarged portion extending laterally therefrom, and mounted within this portion are a pair of normally spaced contacts 29 and 30 which may be L-shaped members as illustrated in FIGURE 2, fixedly secured to the hearing by a cap screw or other suitable means. The contacts are normally spaced, but when the magnet 17 moves downwardly the pad 25 engages the upper contact 29 and presses the same downwardly and into engagement with the contact 30 thereby establishing an electrical connection therebetween. Electrically connected in series with the contacts 29 and 30 is an indicia element in the form of a signal light 31 mounted within the base of the U-shaped frame 10.

The contacts and signal light are electrically connected with a power source such as a battery 32 contained within the hollow handle 11; and thus, closing of the contacts 29 and 30 completes the electrical circuit whereby the light 31 is energized. The lead wires may extend through passages 33 provided in the frame, and such passages communicate with an enlarged opening 34 in which the light is positioned. If the frame and handle are formed of plastic as illustrated in FIGURE 4, a metal sleeve 35 may be inserted Within the handle to effect an electrical connection with the battery 32 through the metal plate 36 and spring 37 to the lead 38. The other lead 39 having the light 31 interposed therein may be connected to the battery through the fixed contact 40 connected to the lead 39.

By reference to FIGURE 6 in particular, it will be seen that the electro-magnet 17 and especially the coil 18 thereof is connected to the battery 32. It will be appreciated that a conventional switch may be interposed in the circuit to interrupt the same and thereby obviate a drain on the battery when the device is not in use. However, for convenience, such a switch is not illustrated, and it will be apparent that the same result may be achieved by loosening the cap 12 to withdraw the battery 32 from 3 the contact therefor positioned at the inner end of the hollow handle.

Substantially the same circuit is employed if a permanent magnet is used instead of the electro-magnet 17, as is apparent from-an inspection of FIGURE 5. The only difference between the two circuits is that there is no need to connect a permanent magnet to the power source. For purposes of differentiation, the permanent magnet in FIGURE 5 is denoted with the numeral 17.

The entire structure may be formed of plastic or other non-magnetic material, and it may be molded in two halves as indicated in FIGURE 1 to permit ready assembly and ease in mounting the various components. Such half sections may then be secured together by any suitable means such as cements, etc. If desired, the light 31 and electro-rrragnet (if such is employed) may be designed to operate from a 110-volt line rather than from the DC. power source shown.

In use of the device, the handle 11 will be gripped in the hand and the cylindrical roller 16 moved over a surface in which a ferrous metal object is concealed. The device should be held so that the magnet 17 is substantially normal to such surface and with the lower arcuate ends of the sections 19-19 adjacent such surface. When a ferrous object is traversed, the magnet will be drawn theretoward, whereupon the contacts 29 and 30 will be closed and the signal light 31 actuated. Thus, the device senses the presence of a ferrous metal object and also the location thereof' While in the foregoing specification embodiments of the invention have been set forth in considerable detail for purposes of making an adequate disclosure thereof, it will be apparent to those skilled in the art that numerous changes may be made in those details without departing from the spin't and principles of the invention.

I claim:

In a detector structure for locating magnetically-susceptible objects normally concealed by a relatively thin covering layer of non-magnetically-susceptible material, a frame equipped with a pair of laterally spaced legs extending longitudinally therefrom in substantially parallel relation, said legs respectively providing a pair of inwardly facing and laterally aligned bearings having a common axis defined therethrough, a hollow substantially cylindrical roller extending between said bearings and being supported thereon for rotation about said common axis and being formed of a non-magnetically-susceptible material, an elongated handle secured to said frame and extending longitudinally therefrom in a direction opposite from said legs and defining a hand-grip to facilitate manipu-lation of said detector structure, said handle being provided with a compartment adapted to receive a battery therein, each of said bearings along the inner facing surfaces thereof and within said roller being provided with a recess, a pair of resilient members respectively constrained within said recesses and being compressible in a common direction substantially normal to. said axis, magnet structure supported within said hollow roller for movement alongsuch common direction between a first position remote from the surface of said roller and a second position displaced theretoward, said magnet structure being equipped with a pair of pins respectively extending laterally outwardly from said magnet structure and into said recesses and seating against said resilient members, said resilient members being effective to bias said magnet stmcture toward such first position thereof remote from the surface of said roller and being compressed by movement of said magnet Structure toward the second position thereof, an electrically actuated signal device carried by said frame to afford sensible indicia to an operator of said detector structure, a normally open circuit including said signal device as a component thereof, and a circuit closure element included in said circuit and being mounted within one of said recesses along the path of movement of said'magnet structure from the first to the second position thereof so as to be operated by the associated pin upon such displacement of said magnet structure toward its second position to close said circuit, said detector structure being movable over relatively large surface areas provided by such concealing layer while said roller is maintained in continuous rolling engagement therewith whereby a magnetically-susceptible object concealed by such layer and traversed by said roller will effect displacement of said magnet structure from its first toward its. second position with the result that said circuit will be closed and said signal device energized to indicate the location of such concealed object.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,755 Drake May 9, 1933 2,637,115 Watson May 5, 1953 2,673,404 Abrahamson i Mar. 30, 1954 2,705,302 Camp et al Mar. 29, 1955 2,749,663 Lemelson June 12, 1956 2,762,970 Balduman Sept. 11, 1956 2,788,484- Deming t Apr. 9, 1957 2,804,518 Cooley Aug. 27, 1-957 

